A2: Thiomersal has also been investigated and no association is found between the two. Vaccines are heavily reviewed for safety beforehand, and since they are given to millions of people each year, even rare complications or problems should become readily apparent. The amount of these additives in each vaccine is minuscule, and not associated with significant side effects in the doses given. Though many parents have advocated for and claimed harm from these additives, without a plausible reason to expect harm, or demonstrated association between autism and vaccination, following these avenues wastes scarce research resources that could be better put to use investigating more promising avenues of research or determining treatments or quality-of-life improving interventions for the good of parents and children.
Specifically regarding "toxins", these substances are often unnamed and only vaguely alluded to - a practice that results in
moving the goalposts. Once it is demonstrated that an ingredient is not in fact harmful, advocates will insist that their real concern is with
another ingredient. This cycle perpetuates indefinitely, since the assumption is generally
a priori that vaccines are harmful, and no possible level of evidence is sufficient to convince the advocate otherwise.